1. Field of the Invention
The present invention relates to scroll-type compressors for use in air conditioning systems. More particularly, this invention relates to scroll-type compressors with improved piston valve mechanisms for controlling circulation of lubricating oil in such compressors.
2. Description of Related Art
Known scroll-type compressors generally have a structure in which a refrigerant, which flows through a refrigeration circuit, is drawn into a suction chamber of the scroll-type compressor. From the suction chamber, the refrigerant is drawn into a compression chamber formed by two scroll elements that cooperate to compress the refrigerant and then to discharge the compressed refrigerant into a discharge chamber. The compressor includes a plurality of slidable parts, e.g., bearing members.
The slidable parts may be lubricated by oil that circulates in the compressor. A portion of the oil accumulates in a liquid state within the compressor, while another portion of the oil exists in a suspended state, e.g., as a mist, and flows with the refrigerant through the compressor. If the accumulated liquid state oil (hereinafter referred to as xe2x80x9clubricating oilxe2x80x9d) is supplied to the slidable parts at an appropriate rate, the slidable parts will be lubricated.
For example, in Japanese Patent Publication Hei 8-177762, a scroll-type compressor is disclosed in which the internal space of the compressor includes a high pressure chamber, a medium pressure chamber, and a low pressure chamber. The pressure differences between these chambers are used to feed lubricating oil to the slidable parts of the compressor. The scroll-type compressor is equipped with a piston valve mechanism for controlling the flow of lubricating oil to the slidable parts. The piston valve mechanism includes a piston valve, which is slidably disposed in a cylinder bore. One end of the cylinder bore is in fluid communication with the low pressure chamber. The other end of the cylinder bore is in fluid communication with the medium pressure chamber. A spring, which is disposed at the low pressure side of the cylinder bore, engages the piston valve and biases it toward a snap ring, which is disposed at the medium pressure side of the cylinder bore. In this way, the refrigerant in the low pressure chamber and the resilient spring urge the piston valve toward the medium pressure chamber, while the refrigerant in the medium pressure chamber urges the piston valve toward the low pressure chamber. The movement of the piston valve opens and closes an oil passage that connects the high pressure chamber to the medium pressure chamber.
The compressor includes slidable parts disposed between the medium pressure chamber and the low pressure chamber. These slidable parts may be lubricated in the following manner. Lubricating oil that is in a suspended state in the suction chamber is drawn into the compression chamber with refrigerant from the refrigeration circuit. The lubricating oil flows through the compression chamber with the refrigerant and then is discharged to the high pressure chamber. A portion of the lubricating oil may accumulate in a liquid state in the high pressure chamber. When the piston valve is positioned to open the oil passage and place the high pressure chamber in fluid communication with the medium pressure chamber, the lubricating oil in the high pressure chamber may flow to the medium pressure chamber via the oil passage due to the pressure difference between the chambers. Subsequently, due to the pressure difference between the medium pressure chamber and the low pressure chamber, the lubricating oil may flow from the medium pressure chamber to the low pressure chamber, thereby lubricating the various slidable parts disposed between the medium chamber and the low pressure chamber.
In known scroll-type compressors, when the pressure difference between the medium pressure chamber and the low pressure chamber is too great, the piston valve may be displaced to such an extent and for such a duration that the spring may be overcompressed, e.g., compressed so that the coils are in contact. If overcompression of the spring occurs repeatedly, the spring may be damaged, e.g., it may lose its elasticity, it may deform, it may break, or the like. If the spring is damaged, the piston valve may not be displaced enough to open the oil passage. As a result, lubrication of the slidable parts may not occur or may be insufficient to prevent damage to the slidable parts.
A need has arisen for scroll-type compressors, in which a piston valve mechanism is driven by a pressure differential and a spring, for an improved mechanism that prevents overcompression of the spring.
In an embodiment of the present invention, a scroll-type compressor, which comprises a piston valve mechanism for controlling a flow of lubricating oil within the compressor, comprises a cylinder bore for establishing fluid communication between a medium pressure chamber and a low pressure chamber, and a piston valve and a spring accommodated within the cylinder bore. Moreover, the piston valve is driven by a pressure difference between the medium pressure chamber and the low pressure chamber, and by a spring that biases the piston valve toward the medium pressure chamber. Further, a stroke limiting mechanism limits movement of the piston valve against the spring.
In another embodiment of the present invention, the stroke limiting mechanism comprises an inwardly stepped, limiting portion formed in the cylinder bore for engaging an end surface of the piston valve.
In still another embodiment of the present invention, the stroke limiting mechanism comprises an outwardly stepped flange formed on the piston valve for engaging a shoulder formed in the cylinder bore.
In yet another embodiment of the present invention, the stroke limiting mechanism comprises a penetrating hole bored through the piston valve and a pin fixed to the compressor housing and inserted through the penetrating hole. Movement of the piston valve is limited by engagement of the pin and an inner wall of the penetrating hole.
In yet a further embodiment of the present invention, the stroke limiting mechanism comprises a rod formed on an end of the piston valve and inserted into the spring. Movement of the piston valve is limited by engagement of the rod and a stopping portion formed at an end of the cylinder bore.
In a still further embodiment of the present invention, the stroke limiting mechanism comprises a relief passage for providing fluid communication between the medium pressure chamber and the low pressure chamber. The piston valve opens the relief passage to reduce a pressure differential between the medium pressure chamber and the low pressure chamber to limit further movement of the piston valve against the spring.
In yet a further embodiment of the present invention, the stroke limiting mechanism comprises a relief passage that provides fluid communication between the medium pressure chamber and the low pressure chamber and a valve mechanism that opens the relief passage when a pressure differential between the medium pressure chamber and the low pressure chamber exceeds a desired level to limit further movement of the piston valve against the spring.
Other objects, features, and advantages of this invention will be apparent to, and understood by, persons of ordinary skill in the art from the following description of preferred embodiments with reference to the accompanying drawings.